CZ230694A3 - Process for producing ultra-high-molecular polyethylene with a high apparent density - Google Patents

Abstract

Ultrahigh-molecular-weight polyethylene of high bulk density is obtained by polymerisation of ethylene in the presence of a mixed catalyst comprising an organoaluminium compound and a titanium component prepared by reduction of Ti(IV) compound followed by treatment of the reduction product with an organoaluminium compound.

Description

The invention relates to a process for the production of ultra-high molecular weight polyethylene (PE-UHMV) having a bulk density of 350 to 460 g / l, in particular 430 to 460 g / l.

BACKGROUND OF THE INVENTION

By ultra-high molecular weight polyethylene is meant linear polyethylene having an average molecular weight of at least 10 [mu] g / mol, especially 2.5. 10 µg / mol to more than 10 ⁷ g / mol. The determination of the above-mentioned molecular weights is carried out according to the solution viscosity according to the Margolies equation. The methods used for the assay are described, for example, in CZ Chemie Technik 4, (1974), p. 129 et seq.

PE-UHMV occupies a special place among the types of polyethylene. It is characterized by a number of physical characteristics that allow its versatile applications. Particularly important are its high abrasion resistance, very low coefficient of friction compared to other materials, excellent toughness and high heat resistance. In addition, it is remarkably resistant to many chemicals.

Because of these particular mechanical, thermal

-2a chemical properties PE-UHMV finds use in various fields of technology as a special high-value material. Examples are the textile industry, mechanical engineering, chemical industry and mining.

Various processes are known for the production of these special types of polyethylene. Low pressure polymerization of ethylene using Ziegler catalysts, i.e. a mixture of compounds IV, has proven to be very useful. to VI. subgroups of the periodic system of elements with organometallic compounds I. to III. groups of the periodic system. Among the compounds of elements IV. to VI. the subgroups are most important titanium compounds.

Most often as organometallic compounds I to III. groups use aluminum alkyls and aluminum alkyl halides.

In most cases, Ziegler catalysts are prepared by reducing Ti (IV) compounds such as titanium tetrachloride or titanium (IV) ester with organoaluminum compounds.

Thereby, Ti (III) compounds are obtained, which are generally isolated, suspended in a suitable composition and mixed with the activator required for the reaction.

According to the tested process, ethylene having an oxygen content of less than 5 ppm at 30 to 130 ^and C and a pressure of 0.1 to 10 MPa is polymerized in the production of PE-UHMV using catalysts containing titanium halides (III) and organic compounds % of aluminum in a molar ratio of 1: 0.2 to 1: 5 and to the reaction mixture during the polymerization are added monohydric aliphatic alcohols in an amount of from 2 to 10 mol, based on 1 kg of catalyst. Diethyl aluminum monochloride (DE-C-2 361 508) was used as the organoaluminum component of the catalyst.

According to another method, an unsaturated polymeric organoaluminium compound, for example isopropylaluminum or myrcenylaluminum, is used as aluminum compounds in the catalyst system (DE-C-2 361 052).

PE-UHMV is mainly used as a raw material. Therefore, the powder morphology and the bulk density derived therefrom are important properties on which its processability depends. Thus, by way of example, the size and shape of the polymer particles and, in addition, depending on the variability in molecular weight distribution, the properties of porous molded bodies which are prepared by sintering from PE-UHMV powder, are the same as in the production of highly modular . But even for the production process itself and for storage, the morphology of the powder is not meaningless. Large particles with narrow grain size distribution and high bulk density require less energy to dry and require less storage space.

The known processes for the production of PE-UHMV allow influencing the external form of polymer particles only within very narrow limits. Accordingly, there has been a need for an operating method that allows the production of powdered, ultra-high molecular weight polyethylene with a narrow granulometry and a targeted bulk density. At the same time, the low process agglomerate and coating in the reactor should ensure high process usability.

Summary of the Invention

This object is achieved by a process for the production of polyethylene powder having a molecular weight of at least 10 [mu] g / mol and a bulk density of from 350 to 460 g / l, in particular 430 to 460 g / l by polymerizing ethylene at temperatures from 30 to 130 [deg. 5 to 4 MPa in the presence of a mixed catalyst consisting of a titanium component and an organic aluminum compound and in the presence of a molecular weight regulator. The process is characterized in that the titanium component is prepared by a two-step reaction, wherein in the first step the titanium compound (IV) is reacted with an organic aluminum compound at a temperature of -40 to 140 ° C at a molar ratio of titanium to aluminum of 1: 0.1 to 1: 0. 6 to form a titanium compound (III) and in a second step, the product of the first reaction is treated with an organic aluminum compound at a temperature of -10 to 150 ° C at a titanium to aluminum molar ratio of 1: 0.01 to 1: 5 an aluminum compound at a titanium to aluminum molar ratio of 1: 1 to 1: 15 produces a mixed catalyst.

The novel process makes it possible to selectively adjust the bulk density of ultra-high molecular weight polyethylene by varying the process for treating the titanium compound (III) from the first reaction step with an organic aluminum compound in the range of 350 to 460 g / l, in particular 430 to 460 g / l. The term bulk density means a value determined in accordance with DIN 53468.

For the production of titanium compounds (III), the first step is based on titanium compounds (IV). Suitable compounds are those of the formula Ti (OR ³ ) 4 - _n X _n wherein n is an integer from 1 to 4, R ³ are the same or different hydrocarbon radicals, especially alkyl radicals having 1 to 18 carbon atoms,

Preferably with 2 to 8 carbon atoms and X is halogen, especially chlorine or bromine. Examples are TiCl _4, TiBr _4, Ti (OC ₂ H ₅₎ Cl _3, Ti (OC _{5 H?)} C1 _3, Ti (Oi-C ₄ H ₉₎ C1 _third The organic aluminum compounds which can be used according to the invention to reduce the compounds (III) correspond to the general formula AIR _{3 m} x _m , where m is 0, 1 or 2; R represents the same or different hydrocarbon radicals, in particular alkyl radicals having 1 to 12 carbon atoms, in particular 2 to 6 carbon atoms, and X represents halogen, in particular chlorine or bromine. Examples of such compounds are triethylaluminum, triisobutylaluminum, diethylaluminum chloride and ethylaluminum dichloride. Also suitable are polymeric organic aluminum compounds obtained by the reaction of lithium aluminum hydride or aluminum trialkyls or aluminum dialkyl hydrides, the alkyl radicals of which each contain from 1 to 16 carbon atoms, with diolefins C ₄ -C ₁₂ , in particular diolefins C ₄ -C ₁₂ . These, in contrast to mononuclear trialkylaluminum compounds and alkylaluminium hallogenides, are multinuclear. Preferably, reaction products of A1 (i-C ₄ Hq) ₃ or Al (iC ₄ H _{9) 2} H with isoprene (isoprenylaluminum). The aluminum compounds can be used in pure form or also as mixtures of two or more compounds.

The reaction of Ti (IV) compounds with organic aluminum compounds is carried out in an inert solvent at temperatures from -40 to 140 ° C, preferably -20 to 120 ° C. The concentration of the reactants in the starting solutions is 0.1 to 9.1 moles of Ti (IV) per solvent and 0.05 to 1.0 moles of aluminum compound per solvent, in particular 5.0 to 9.1 moles of Ti (IV) ) and 0.2 to 0.9 mol of aluminum compound, in each case per solvent. 0.1 to 0.6 mol, preferably 0.3 to 0.5 mol, of aluminum is used per mole of Ti (IV)

-6organic aluminum compounds. Aliphatic hydrocarbons have proved to be inert solvents. Depending on the temperature, the reaction is complete after 1 to 600 minutes. The degree of reduction to be measured in a manner that is cerimically determined is at least 95%.

The reduction is carried out according to the invention as a second stage of treatment of the reduction product with an organic aluminum compound. To this end, it is filtered from the suspension, washed with a solvent or suspending agent and resuspended in an inert organic solvent. However, the suspension obtained in the reaction may also be used immediately.

Such a procedure is recommended whenever the reduction of Ti (IV) with an aluminum compound is carried out in a titanium to aluminum molar ratio of about 1: 0.5.

For further processing, the reaction product is reacted with an organic aluminum compound which is added as a solution or suspension. The reactants are allowed to interact with stirring for 1 to 1200 minutes and at temperatures from -10 to 150 ° C, preferably 0 to 70 ° C. The organic aluminum compounds used are mono- or polynuclear mono- or dialkylaluminum halides or trialkylaluminum compounds. Preferably, isoprenylaluminum is used to prevent unnecessary reduction and thereby inhibition of the catalyst. Viewed, the reaction is recognizable by deepening the color of the titanium compound from reddish brown to brownish black. As investigations have shown, this is not due to the continued reduction of the compounds (III) but to the irreversible increase in the molar ratios of aluminum to titanium in the solid. While this ratio in the reduction product is from 0.2 to 0.33: 1, it increases to about 0.4 to 0.6: 1 during the treatment with the organic aluminum compound.

- during processing, reaction time, aluminum alkyl reduction potential and reaction temperature. Usually, the molar ratio of titanium to aluminum is maintained at 1: 0.01 to 1: 5, preferably 1: 0.4 to 1: 1.2. The molar ratio of aluminum to titanium in the processing product (titanium component) determines the morphology of the polymer and thereby the grain size distribution and bulk density of the polymer. The titanium-aluminum molar ratios in the lower region yield bulk densities below 400 g / l, in the upper region densities from 430 to 460 g / l. The catalyst slurry thus obtained can be used immediately or after filtration and optionally washing with the slurry.

To prepare the catalyst, the titanium component is activated with an organic aluminum compound. As the reduction, the aluminum compound can be used in pure form or also as a mixture of two or more compounds, preferably an aluminum triisobutyl or aluminum isoprenyl activator. The molar ratio of titanium (based on the amount of titanium initially used as Ti (IV)) to aluminum is 1: 1 to 1: 15, preferably 1: 2 to 1: 10.

The polymerization is carried out in suspension in one or more stages continuously or also batchwise at temperatures from 30 to 130 ° C, preferably 60 to 100 ° C and at an ethylene partial pressure of less than 4.0 MPa, preferably 0.05 to 0, 8 MPa.

Suitable reaction medium for polymerization are the inert solvents commonly used for the low pressure Ziegler process, such as aliphatic or cycloaliphatic hydrocarbons, for example butane, pentane, hexane, cyclohexane, nonane and decane. In addition, gasoline fractions or hydrogenated diesel oil fractions which have been carefully freed from it may also be used

-8 Oxygen, sulfur compounds and moisture. Their boiling point is between -5 and 220 ° C, preferably between 65 and 180 ^e C.

The molecular weights of the polymers can be predetermined in a known manner by molecular weight regulators, preferably hydrogen. The ratio of the ethylene partial pressure to the hydrogen partial pressure is at least 10, preferably 40 to 1600.

The polymer is separated from the suspending agent and dried under an inert gas. Excluding air and moisture, the suspension composition is reused for polymerization without any treatment.

DETAILED DESCRIPTION OF THE INVENTION

In the following examples, the invention will be described in more detail, but is not limited to the embodiments.

The following values are given to describe the polymer:

mean grain diameter - determined by laser beam bending using a Helos-Rhodos grain size analyzer and Sympatec GmbH measuring and evaluation system; optical concentration of about 10%.

s-value - serves as a measure of grain distribution width and results from formula d (90) s = log d (10) where d (90) and d (10) are grain sizes obtained

-9 from the cumulative aggregate grain size distribution at 90% and at 10%; s increases with increasing grain size distribution width.

ZST or creep value - serves as a measure of molecular weight and is determined according to DIN 53 493;

Bulk density - determined according to DIN 53 468.

Example 1

1.1. Production of base catalyst (prior art catalyst)

To 230 l of a 20% by weight isoprenylaluminium (IPRA) solution in 200 mol of hexane, 44.1 l of titanium tetrachloride (corresponding to a ratio of 1 mol of titanium to 0.5 mol of aluminum) is metered in under an inert atmosphere at -10 ° C over 7 hours. ).

The reaction was complete after 3 hours. More than 96% of the Ti (IV) used is reduced to Ti (III).

1.2. Polymerization using the catalyst produced according to 1.1.

The polymerization is carried out in a continuously operated apparatus in a one-stage process at reflux of the reaction medium. Gasoline purified through a molecular sieve with a boiling range up to 140-170 ° C serves as a suspending agent.

At a reaction temperature of 80 ° C and a yield of 1.7 kg PE / mmol Ti, based on the catalyst used, the ethylene partial pressure is adjusted to 0.32 MPa. The hydrogen content of the gas phase is about 0.5% by volume. The ratio of suspending agent to polyethylene (in 1 / kg) is 4.3. The concentration of activator (= IPRA) in the reaction mixture introduced into the reactor is determined such that the molar ratio of aluminum component to titanium component (based on the amount of titanium originally used as Ti (IV)) in the reactor is about 1: 10. by controlling the hydrogen content of the gas phase in the reactor. In two parallel experiments (A and B) the following product properties are reproducibly reproduced:

Experiment A Experiment B

mean grain diameter (gm) 210 200 s-value 0.51 0.51 bulk density (g / L) 370 380 value ZST (M / mm ² ) 0.24 0.24

Example 2

2.1. Production of a catalyst according to the invention

The catalyst (KO) described in 1.1. will be diluted to ί »wjTwmtsTK! * ··’. ’

A concentration of the titanium component of 40 mmol / l and at room temperature is treated with IPRA (K1 to K6). Depending on the amount of aluiminium alkyl used, the coloration increases from reddish brown to dark brown. The degree of reduction remains unchanged.

In contrast, the content of chemically bound aluminum in the solid phase of the catalyst rises from 0.2 to 0.33: 1 to 0.6: 1. To determine this value by atomic absorption spectroscopy, the catalyst is filtered off under shielding gas and washed twice with petrol.

Designation Catalyst Processing Bound Al Catalyst Ti All: AI Ti: AI

KO 0 1: : 0,32 Kl 1: 0.05 1: : 0,21 K2 1: 0.1 1: : 0,23 K3 1: 0.5 1: : 0,55 K4 1: 1 1: : 0,45 K5 1: 2 1; : 0,5 K6 1: 5 1: : 0,4

The catalyst was used for polymerization after a reaction time of 24 hours. K6 documents that the use of larger amounts of an organic aluminum compound under otherwise identical conditions does not lead to an increase in the proportion of aluminum in the titanium component.

-122.2. Polymerization using the catalyst produced according to 2.1.

2.2.1. Use of non-separated catalyst

The synthesis of PE-UHMV is analogous to that described in 1.1. use catalysts of types K3 and K5 immediately after preparation, i.e., unfiltered and washed. Compared to the reference catalyst KO, the reaction temperature is lowered to about 78 ° C and the molar ratio of aluminum (IPRA) to the titanium component in the reactor is lowered to about 3.0 to achieve an ethylene partial pressure of about 0.25 MPa. The hydrogen content is set as in 1.2.

2.2.2. Use of a pre-separated catalyst

The polymerization is carried out as described in 2.2.1. A K4 catalyst is used, which is filtered off and washed with a suspending agent before use.

Results of polymerization experiments:

mm.?···-;*- ',. · - · · · · ·

Type of catalyst: K3 K4 K5 K0 ^X Yield (kg PE / mmol Ti) 1.1 2.8 3.3 1.7 Mean grain diameter (gm) 150 160 180 210 s —value 0.43 0.39 0.43 0.51 bulk density (g / 1) 450 460 445 370 ZST (Nmm ² ) 0.24 0.24 0.24 0.24

γ reference experiment 1.2.

Claims (8)

Process for producing polyethylene powder having a viscosimetrically measured molecular weight of at least 10 µg / mol and a bulk density of from 350 to 460 g / l, in particular of 430 to 460 g / l, polymerization of ethylene at temperatures of 30 to 130 ° C and pressures of 0, 5 to 4 MPa in the presence of a mixed catalyst consisting of a titanium component and an organic aluminum compound and in the presence of a molecular weight regulator, characterized in that the titanium component is prepared by a two-step reaction. at a temperature of -40 to 140 ° C at a titanium to aluminum molar ratio of 1: 0.1 to 1: 0.6 to give a titanium compound (III) and in a second step the product of the first reaction is treated with an organic aluminum compound at -10 to 150 ° C at a molar ratio of titanium to aluminum of 1: 0.01 to 1: 5 and a titanium component with an organic aluminum compound at a molar ratio titanium to aluminum A mixed catalyst is prepared from 1: 1 to 1:15. ² Method according to claim 1, characterized in that the titanium compound used in the first step corresponds to the general formula Ti (OR 1) 4 _n x _n , wherein n is an integer from 1 to 4, R @ ¹ are the same or different hydrocarbon radicals, especially alkyl radicals having 1 to 18 carbon atoms, preferably 2 to 8 carbon atoms and an organic aluminum compound -15 corresponds to the general AIR formula 3 _nj X _m , wherein m is 0, 1 or 2; »R ² represents identical or different hydrocarbon radicals, in particular alkyl radicals having 1 to 12 carbon atoms, especially 2 to 6 carbon atoms and X is halogen, especially chlorine or bromine, or an organic aluminum compound is a polyaluminium compound, in particular isoprenylaluminum. - - 3. The method according to claim 1 or 2, characterized in that the reaction between the titanium compound (IV) and the compound of aluminum is carried out at temperatures from -20 to 120 ^e C Method according to one or more of Claims 1 to 3, characterized in that 0.3 to 0.5 mol of aluminum is used per mol of titanium (IV) in the form of an organic aluminum compound. Process according to one or more of Claims 1 to 4, characterized in that the titanium compound (III) obtained in the first stage is treated in the second stage with mono- or polynuclear mono- or dialkylaluminum halide or with trialkylaluminum compounds. Method according to one or more of Claims 1 to 5, characterized in that the titanium compound (III) from the first stage is filtered off and washed with an inert solvent before further treatment. Method according to one or more of Claims 1 to 6, characterized in that the molar ratio of titanium to aluminum in the second stage is 1: 0.01 to 1: 5, preferably 1: 0.4 to 1: 1.2 . -168. Process according to one or more of Claims 1 to 7, characterized in that a mixed catalyst with an organic aluminum compound, in particular aluninium triisobutyl or aluminum isoprenyl, is prepared from the titanium component obtained in the second stage. Method according to claim 8, characterized in that the organic aluminum compound and the titanium component are used in a molar ratio of 1: 1 to 15: 1, preferably 2: 1 to 10: 1.